CVE-2007-1359 in mod_security
Summary
by MITRE
Interpretation conflict in ModSecurity (mod_security) 2.1.0 and earlier allows remote attackers to bypass request rules via application/x-www-form-urlencoded POST data that contains an ASCIIZ (0x00) byte, which mod_security treats as a terminator even though it is still processed as normal data by some HTTP parsers including PHP 5.2.0, and possibly parsers in Perl, and Python.
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Analysis
by VulDB Data Team • 02/06/2025
The vulnerability described in CVE-2007-1359 represents a critical interpretation conflict within the ModSecurity web application firewall implementation that affects versions 2.1.0 and earlier. This flaw stems from a fundamental mismatch in how ModSecurity processes application/x-www-form-urlencoded POST data compared to how standard HTTP parsers handle the same data. The core issue manifests when ASCIIZ null bytes (0x00) are present within the POST payload, creating a scenario where ModSecurity's internal parsing logic treats these bytes as data terminators while other parsers continue to process them as legitimate content.
The technical exploitation of this vulnerability occurs through a specific parsing inconsistency where ModSecurity's rule engine terminates its processing of POST data upon encountering a null byte, effectively truncating the data before it can be fully evaluated against security rules. Meanwhile, other HTTP parsers such as PHP 5.2.0, Perl, and Python continue to process the complete payload including the null bytes, leading to a scenario where malicious content can bypass security controls. This interpretation conflict creates a dangerous gap in the security posture where data that should be subject to comprehensive rule evaluation is instead partially ignored by ModSecurity's processing logic.
The operational impact of this vulnerability extends beyond simple bypass capabilities to represent a significant threat to web application security. Attackers can craft malicious POST requests containing null bytes that will be processed correctly by web application servers while simultaneously being truncated by ModSecurity, allowing malicious payloads to pass through security controls undetected. This creates a scenario where ModSecurity's protection mechanisms become ineffective against specifically crafted attacks, potentially enabling data exfiltration, command injection, or other malicious activities that would normally be blocked by the firewall's rule set. The vulnerability particularly affects applications that rely heavily on form data processing and where ModSecurity is configured to monitor or filter POST requests containing user-supplied data.
From a cybersecurity framework perspective, this vulnerability aligns with CWE-129 and CWE-130 categories related to improper input validation and insufficient input sanitization, while also mapping to ATT&CK techniques involving command and control communications and execution through web shells. Organizations implementing ModSecurity for web application protection face a critical risk where their security controls become ineffective against specifically crafted payloads. The vulnerability demonstrates the importance of consistent data interpretation across security tools and the potential for seemingly minor parsing differences to create significant security gaps. Remediation requires immediate upgrading to ModSecurity versions that address this parsing inconsistency, along with thorough testing of existing security rules to ensure proper handling of edge cases in data processing.
The broader implications of this vulnerability highlight the challenges inherent in maintaining consistent security across complex web application environments where multiple parsers and processing layers interact. It underscores the need for comprehensive testing of security controls against edge cases and the importance of understanding how different components in a web stack handle identical data inputs. Organizations must consider implementing additional monitoring and validation mechanisms to detect potential bypass attempts and ensure that their security tooling maintains consistent behavior across all data processing scenarios. This vulnerability serves as a critical reminder that even subtle differences in data interpretation can create exploitable gaps in security infrastructure.